Did it!
The music was working and by the time Bruno Mars was telling me he was dripping with Finesse and I was dripping with sweat I was half way through, then had Cee Lo Green in love with the girl who left him for someone richer (get over it Cee Lo!) and Jocelyn Brown in love with Someone Else's Guy (same advice!) I realised I had actually run over the 28 mins and done 30 mins - which I was very happy about. If I had more time I could have run more, it felt good.
BUT, at around 20 mins, I had a twinge for a few seconds in the back of my left thigh...I rubbed it and relaxed the muscle in between steps (must have looked awkward but it worked). As it went away I carried on but anything I should be looking out for? Should I stick some cream on it during the night tonight?